1. Field of the Invention
This invention relates to the use of a weak acid cation exchange resin in reducing the sodium/ammonium alkalinity of industrial/municipal wastewater.
2. Brief Description of Disclosures In The Art
There is currently a growing need to operate with zero discharge wastewater in many large scale industrial processes located in arid regions, such as the Southwest, and in areas where federal and state regulatory schemes are uncertain regarding amounts and quality of generated process wastewater. By the term "zero discharge" is meant that generated wastewater in a process is not discharged, but treated to reduce/remove pollutants and then recycled back into the process for a variety of uses, such as process makeup cooling water, i.e., supplemental cooling water to replace that lost by evaporation.
Wastewater reduction schemes are particularly necessary in large scale hydrocarbon conversion processes, such as coal liquefaction, i.e., Exxon Donor Solvent.TM. coal liquefaction process. Wastewater in a typical coal liquefaction process contains copious amounts of dissolved organic materials such as phenols, organic acids, organic nitrogen compounds, ketones, aldehydes and dissolved ammonia. This wastewater effluent can be initially treated with means to remove hydrogen sulfides, volatile and steam-distillable organics and a large portion of the ammonia. Caustic can then be added to produce free ammonia and a portion of this residual ammonia can be further removed by steam. The phenolics can then be extracted by suitable processes. Following extraction of phenolics, the wastewater can be biologically treated with microorganisms ("biox-treated") to degrade dissolved organics, while also removing nutrient salts, such as ammonia and other nitrogen compounds. Following the biological treatment, the treated wastewater is filtered to remove particulate matter not susceptible to removal by biological treatment.
Following filtration, the treated wastewater can optionally be treated with activated carbon to remove non-degradable organic compounds by adsorption.
At this point, the biologically treated wastewater contains a high amount of sodium alkalinity, a high total alkalinity and relatively low ammonia alkalinity. To be classified a makeup cooling water, the total alkalinity and sodium alkalinity must be substantially decreased to avoid corrosion to the downstream carbon steel equipment. Further, the residual ammonium alkalinity must be further minimized since the wastewater has to be chlorinated prior to recycle to avoid undesirable sludge formation. Each unit weight of ammonium requires about 10 unit weight chlorine to adequately control biological growth in recirculated cooling water and excessive amounts of residual ammonia can lead to excessive costs in the chlorination step.
Strong acid Cation resin exchange procedures are known in the art for reducing total alkalinity, sodium alkalinity, and ammonium alkalinity. However, the use of a strong cation exchange resin would unnecessarily add to the cost of any process based thereon, since strong mineral acid would be generated in the cation exchange scheme necessitating a further downstream neutralization step.
Weak acid and cation ion exchange resins are know to be effective for removing individually sodium or ammonium alkalinity from wastewater by exchange with hydrogen ion.
For example, U.S. Pat. No. 3,475,330 discloses removing ammonia ions from steam condensates by passing the water through a weak acid ion exchange resin.
U.S. Pat. No. 3,928,192 discloses removing water soluble inorganic salts from water by treatment with a combination of weak basic anionic exchange columns, and ammonium-buffered weak cation exchange resins.
U.S. Pat. No. 4,083,782 discloses removing the hardness from water by passing the water through a weak cation exchange resin in the alkali metal or ammonium form.
U.S. Pat. No. 4,349,442 discloses individually removing ammonium and sodium ions from water by passing the water through a cation exchange resin and then through a bed of mixed anion and cation exchange resins.
U.S. Pat. No. 4,370,234 discloses passing wastewater through a biological filter and then ion exchanging the water with a cation exchange resin containing nitrifying bacteria.
Further disclosures in the art include Japanese Pat. Nos. J53101-845 and J56053-743; Russian Pat. SU No. 944-634; U.S. Pat. No. 4,098,690; and U.S. Pat. No. 3,095,265.
As is seen, removing ammonium ions and sodium ions individually by ion exchange procedures utilizing a weak acid cation exchange resin is disclosed by the above-cited disclosures. However, what is desired is a process for simultaneously reducing the concentrations of both ions on the same weak cation exchange resin from industrial/municipal wastewater containing high total alkalinity and sodium alkalinity and relatively low ammonium alkalinity. Thus, alkalinity and ion levels could be obtained sufficient to enable the use of said wastewater after effective chlorination for use, as for example, makeup cooling water, in an industrial process, which does not exhibit significant corrosion or sludge buildup.